Restoring Cloud Access when it's attached to an account that no longer exists on a UniFi controller

If a UniFi controller is stuck in a perpetual state of Connecting under Cloud Access Status, and it's not related to firewall or DNS issues preventing connection back to the Ubiquiti cloud, and no options to turn off Cloud Access are visible on the Cloud Access settings page, there may be leftover cloud access configuration on a previously existing user account that is no longer associated with any current site.

This solution requires manipulation of the UniFi controller's database. If you're not comfortable working with the mongo CLI, do not attempt the following steps. Take a full backup of your UniFi controller before proceeding!